A. Field of Invention
The present invention relates generally to linkage mechanisms for power transfer from a reciprocating power source to a crankshaft, and more particularly to a new and improved means for varying the stroke and power output of a reciprocating power source.
B. Description Of Related Art
In engines with one or more sources of reciprocating power, the power source is frequently a piston and it is frequently desireable to translate the linear motion of the piston and piston rod to the rotary motion of a crankshaft. When the piston rod or pitman directly attaches the piston to the crankshaft, there is little or no possibility of varying the travel range or stroke of a piston nor any way of changing the mechanical advantage between the piston and the crankshaft. Both the piston stroke and the mechanical advantage may be accomplished by means of a linkage arrangement between the power source and the crankshaft. In order to provide a variation in the stroke or in the power output, a pivoting lever sometimes called sway bar, swing beam or rocker beam may be interposed between the piston rod and the crankshaft. The resulting lever system may provide a means for varying the stroke and thereby changing the compression ratio and/or power output by varying the location of the fulcrum point along the rocker beam. Examples of such mechanisms are shown in U.S. Pat. No. 1,189,312 to Tibbels and in U.S. Pat. No. 2,873,611 to Biermann. These patented devices for varying the fulcrum point all rely on an external means, for example, a lever for locating a pivotable slide or cage that may be fixed or partially fixed relative to the piston and crankshaft but is not positively located in a fixed location on the rocker beam itself. As a result, the rocker beam is free to move within the cage or slide and the strain borne by the fulcrum is transferred and borne to the end of the lever controlling the position of the fulcrum. In such systems, the variability of the location of the fulcrum point on the rocker beam would be expected to cause difficulty in attempting accurate control of the stroke and mechanical advantage. In addition, location of the fulcrum point at the end of a lever would significantly increase the force on the mechanism used to control the fulcrum point. Nor are such mechanisms readily and efficiently adapted for use in a multiple piston engine where common and precise control is advantageous.